AMP deaminase is also called adenyl deaminase, AMP aminohydrolase, and the like, and catalyzes a reaction of allowing adenylic acid to hydrolytically deaminate to generate inosinic acid and ammonia. It has been reported that AMP deaminase has been widely found in living animal tissues and separated from various tissues from various species to date (Fujishima T. and Yoshino H., Amino Acid-Nucleic Acid, Vol. 16, pp 45-55 (1967): non-patent document 1, Magdale'na Rosinova' et al., Collection Czechoslov. Chem. Commun. Vol. 43, pp 2324-2329 (1978): non-patent document 2, Japanese Patent Unexamined Publication No. S55-120788: patent document 1). Meanwhile, mainly from the viewpoint of industrial utilization, search for AMP deaminases derived from microorganism has been extensively carried out. Particularly, many studies have been done on AMP deaminase derived from filamentous bacterium. Some AMP deaminases, for example, AMP deaminase derived from Aspergillus melleus have been attempted to be industrially used aiming at increasing taste in production of yeast extract.    Patent document 1: Japanese Patent Unexamined Publication No. S55-120788    Non-patent document 1: Fujishima T. and Yoshino H., Amino Acid-Nucleic Acid, Vol. 16, pp 45-55 (1967)    Non-patent document 2: Magdale'na Rosinova' et al., Collection Czechoslov. Chem. Commun. Vol. 43, pp 2324-2329 (1978)